A typical and known vehicle seat belt system is a three-point continuous loop seat belt system. A three-point continuous loop seat belt system includes a seat belt retractor and a length of belt webbing. The belt webbing extends from the retractor through a D-ring fixed to the vehicle and then down to an anchor point near the vehicle floor. A tongue assembly is slidable (freely moveable) along the length of belt webbing between the D-ring and the anchor point. To use the seat belt system, a vehicle occupant grasps the tongue assembly, pulling the belt across his/her body, and inserts a portion of the tongue assembly into a buckle. When the tongue assembly is fastened in the buckle, a first portion of the belt webbing extends across the lap of the vehicle occupant and a second portion of the belt webbing extends diagonally across the torso of the vehicle occupant. When the tongue assembly is released from the buckle, the belt webbing is rewound by the retractor.
The tongue assembly needs to slide freely along the belt when the occupant moves the tongue assembly toward the buckle to provide simple and convenient belt length adjustment because not all drivers or passengers are the same size, and to compensate for clothing thicknesses such as the use of jackets in the winter. The tongue assembly should also slide along the belt after the occupant unlocks the tongue assembly from the buckle so that the retractor can fully wind up the belt. The retractor would otherwise carry the tongue assembly upwardly to the D-ring, whereupon further movement of the belt would be prevented as the D-ring would block further movement of the tongue assembly. Free movement of the belt webbing through the tongue is also critical since locking or tightening of the shoulder belt portion must lock or tighten the lap belt portion.
In most modern vehicle seat belt systems, the seat belt retractor remains “unlocked” or “loose” at all times unless the seat belt system detects an impending impact. This permits slack in both the shoulder belt and lap belt portions. The objectives of allowing the slack are: (1) to permit driver or passenger comfort and (2) to allow the driver or passenger the ability to reach forward (e.g., to adjust a radio) without having to loosen or unbuckle the seat belt. However, in the event of an accident, the seat belt retractor locks, thus preventing further forward motion of the occupant during deceleration. In many modern systems, a “pre-tensioner” mechanism proactively tightens the seat belt by retracting the shoulder belt under great force for increased occupant restraint. The pre-tensioning retraction of the shoulder belt also tightens the lap belt portion because the continuous belt web slides freely through the tongue. This is an important safety feature intended to provide lower body restraint.
The above-described genres of typical seat belts have numerous failings in several common areas of seat belt use: during high performance and off-road driving, loose lap belts allow the driver and passengers to slide in their seats, thus causing loss of optimum vehicle control; loose lap belts allow “slumping” or “slouching” which can become tiring and induce fatigue during multi-hour trips; and when a child seat is used, loose lap belts permit unsafe seat movement and potentially dangerous stability situations. In all common events, the slack of the typical seat belt design fails to provide a desired degree of controllable restraint in non-accident situations because the lap belt portion is loose.